6,261 research outputs found
3D printing dimensional calibration shape: Clebsch Cubic
3D printing and other layer manufacturing processes are challenged by
dimensional accuracy. Several techniques are used to validate and calibrate
dimensional accuracy through the complete building envelope. The validation
process involves the growing and measuring of a shape with known parameters.
The measured result is compared with the intended digital model. Processes with
the risk of deformation after time or post processing may find this technique
beneficial. We propose to use objects from algebraic geometry as test shapes. A
cubic surface is given as the zero set of a 3rd degree polynomial with 3
variables. A class of cubics in real 3D space contains exactly 27 real lines.
We provide a library for the computer algebra system Singular which, from 6
given points in the plane, constructs a cubic and the lines on it. A surface
shape derived from a cubic offers simplicity to the dimensional comparison
process, in that the straight lines and many other features can be analytically
determined and easily measured using non-digital equipment. For example, the
surface contains so-called Eckardt points, in each of which three of the lines
intersect, and also other intersection points of pairs of lines. Distances
between these intersection points can easily be measured, since the points are
connected by straight lines. At all intersection points of lines, angles can be
verified. Hence, many features distributed over the build volume are known
analytically, and can be used for the validation process. Due to the thin shape
geometry the material required to produce an algebraic surface is minimal. This
paper is the first in a series that proposes the process chain to first define
a cubic with a configuration of lines in a given print volume and then to
develop the point cloud for the final manufacturing. Simple measuring
techniques are recommended.Comment: 8 pages, 1 figure, 1 tabl
A Parallel Tree code for large Nbody simulation: dynamic load balance and data distribution on CRAY T3D system
N-body algorithms for long-range unscreened interactions like gravity belong
to a class of highly irregular problems whose optimal solution is a challenging
task for present-day massively parallel computers. In this paper we describe a
strategy for optimal memory and work distribution which we have applied to our
parallel implementation of the Barnes & Hut (1986) recursive tree scheme on a
Cray T3D using the CRAFT programming environment. We have performed a series of
tests to find an " optimal data distribution " in the T3D memory, and to
identify a strategy for the " Dynamic Load Balance " in order to obtain good
performances when running large simulations (more than 10 million particles).
The results of tests show that the step duration depends on two main factors:
the data locality and the T3D network contention. Increasing data locality we
are able to minimize the step duration if the closest bodies (direct
interaction) tend to be located in the same PE local memory (contiguous block
subdivison, high granularity), whereas the tree properties have a fine grain
distribution. In a very large simulation, due to network contention, an
unbalanced load arises. To remedy this we have devised an automatic work
redistribution mechanism which provided a good Dynamic Load Balance at the
price of an insignificant overhead.Comment: 16 pages with 11 figures included, (Latex, elsart.style). Accepted by
Computer Physics Communication
Social presence in the 21st Century: an adjustment to the Community of Inquiry framework
The Community of Inquiry framework, originally proposed by Garrison, Anderson and Archer (2000) identifies teaching, social and cognitive presences as central to a successful online educational experience. This article presents the findings of a study conducted in Uruguay between 2007 and 2010. The research aimed to establish the role of cognitive, social and teaching presences in the professional development of 40 English language teachers on Continuous Professional Development (CPD) programmes delivered in blended learning settings. The findings suggest that teaching presence and cognitive presence have themselves 'become social'. The research points to social presence as a major lever for engagement, sense-making and peer support. Based on the patterns identified in the study, this article puts forward an adjustment to the Community of Inquiry framework, which shows social presence as more prominent within the teaching and cognitive constructs than the original version of the framework suggests
Shear-banding in a lyotropic lamellar phase, Part 2: Temporal fluctuations
We analyze the temporal fluctuations of the flow field associated to a
shear-induced transition in a lyotropic lamellar phase: the layering transition
of the onion texture. In the first part of this work [Salmon et al., submitted
to Phys. Rev. E], we have evidenced banded flows at the onset of this
shear-induced transition which are well accounted for by the classical picture
of shear-banding. In the present paper, we focus on the temporal fluctuations
of the flow field recorded in the coexistence domain. These striking dynamics
are very slow (100--1000s) and cannot be due to external mechanical noise.
Using velocimetry coupled to structural measurements, we show that these
fluctuations are due to a motion of the interface separating the two
differently sheared bands. Such a motion seems to be governed by the
fluctuations of , the local stress at the interface between the
two bands. Our results thus provide more evidence for the relevance of the
classical mechanical approach of shear-banding even if the mechanism leading to
the fluctuations of remains unclear
Shear-banding in a lyotropic lamellar phase, Part 1: Time-averaged velocity profiles
Using velocity profile measurements based on dynamic light scattering and
coupled to structural and rheological measurements in a Couette cell, we
present evidences for a shear-banding scenario in the shear flow of the onion
texture of a lyotropic lamellar phase. Time-averaged measurements clearly show
the presence of structural shear-banding in the vicinity of a shear-induced
transition, associated to the nucleation and growth of a highly sheared band in
the flow. Our experiments also reveal the presence of slip at the walls of the
Couette cell. Using a simple mechanical approach, we demonstrate that our data
confirms the classical assumption of the shear-banding picture, in which the
interface between bands lies at a given stress . We also outline
the presence of large temporal fluctuations of the flow field, which are the
subject of the second part of this paper [Salmon {\it et al.}, submitted to
Phys. Rev. E]
Comprehensive stellar seismic analysis: A preliminary application of Whosglad to 16 Cygni system
We present a first application of Whosglad method to the components A and B
of the 16 Cygni system. The method was developed to provide a comprehensive
analysis of stellar oscillation spectra. It defines new seismic indicators
which are as uncorrelated and precise as possible and hold detailed information
about stellar interiors. Such indicators, as illustrated in the present paper,
may be used to generate stellar models via forward seismic modeling. Finally,
seismic constraints retrieved by the method provide realistic stellar
parameters.Comment: 4 pages, 3 figures. Proceedings of the meeting Physics of Oscillating
Stars (PHOST), Banyuls-sur-mer, France, 2-7 September 2018 (Session First
Posters Session), published on December 1st 201
On-road driving studies to understand why drivers behave as they do at regional rail level crossings
Variability in decision-making and critical cue use by different road users at rail level crossings
Collisions at rail level crossings (RLXs) are typically high-severity and high-cost, often involving serious injuries, fatalities and major disruptions to the transport network. Most research examining behaviour at RLXs has focused exclusively on drivers and consequently there is little knowledge on how other road users make decisions at RLXs. We collected driversâ, motorcyclistsâ, bicyclistsâ and pedestriansâ self-reported daily experiences at RLXs for two weeks, focusing on behaviour, decision-making and information use in the presence of a train and/or activated RLX signals. Both information use and behaviour differed between road users. Visual information (e.g., flashing lights) was more influential for motorists, whereas pedestrians and cyclists relied more on auditory information (e.g., bells). Pedestrians were also more likely to violate active RLX warnings and/or cross before an approaching train. These results emphasise the importance of adopting holistic RLX design approaches that support cognition and behaviour across for all road users.Practitioner summary: This study explores how information use and decision-making at rail level crossings (RLXs) differs between road user groups, using a two-week self-report study. Most users make safe decisions, but pedestrians are most likely to violate RLX warnings. Information use (visual vs. auditory) also differs substantially between road user groups
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